Process for finishing leather



J. B. WELCH ET m.

PROCESS FOR FINISHING LEATHER Filed Jan. 19, 1925 1|... I ||||Jl||| lllllllllllllllllllll Patented Appr. 6, llQZQ unir l aras rlric;

rar .ii

WILLIAM c. Wenen, or NEWTON,

PROCESS FR FINISHING LEATHER.

application nea ranuar'y'ie; i925; semaine. 3,271.

To all whom 'it' may concern:

Be it known that we, JOHN B. `WELCH and WILLIAM C. llTELoH, citizens of .the United States,`and residents, respectively, of New lrleans, in the parish of Gileans and State of Louisiana, and of Newton, in the county of Middlesex and State of Massachusetts (whose post-oilice addresses are, respectively, 373 Audubon St., New Orleans, and South St., Waltham), have invented certain new and useful improvements in the Processes for Finishing: Leather; and they do hereby declare the following to be a full, clear, and exact description of the invention, suc-h aswill enable others skilled in the art to which it appertains to make and use thesarne.

This invention Arelates to av process for nishing leather, and particularly to a process for making patent leathen 1 rlhe object of the invention is to provide a novel and superior process for finishing the leather, and particularly for making patent leather, by which linishedleather of superior quality character of grain, appear-' rmay be produced at.

ance and Workability a mmimum manufacturing cost.

To this end the invention'consists in the, process hereinafter described and particularly defined in the claims at the end of this specification.

'lhe drawing diagrammatically illustrates the apparatus which it is preferred to utilize in practicing the present process; l

lFig. l is a longitudinal vertical sect1on and l? ig. 2 is a transverse vertical section.

ln the processes heretofore employed for linishing leather,such, for example, as the process for makingpatentleather, the tanned hides in the condition lin which they are received from the tanners are stretched4 or secured in open wooden frames by means of toggle. strings secured to ditl'erent marginal portions of the hides, and which are tacked to the frame. An initial or so-calledl daub coat of coating material is then applied and spread evenly over the surface of the hide,

and in this condition the hides are then placed in the sun in an 'open yard to permit the daub coat to harden, an operation which consumes approximately five hours. some instances, the daub coat is dried by circulation and artificial heat in closed chamhers at temperatures of approximately 130 F. Aftergthe daub lcoat has hardened asecond or finishing coat isapplied directly over Athe daub coat, and the frame with the hides are placed in ovens and the coat baked until v hardened at a temperature ofapproximately 140C? F. The' action of the sun and the ex.

posure to the heat and also 'the bakingwithin the oven operates to shrink .the leather duringthe first portion of the drying or L hardening of the coatings, and before the o5 coating has hardened so that the finished coating is bonded to the hide in a shrunken condition of the latter.A The extent of shrinking of the leather varies accordingto the condition and quality of the hide, but

on an average the area ofthe hide decreases 1n the neighborhood of 2% with each drying, and as a result the finished leather has an area in the neighborhood of 4% to 5% less than the original area of the hide in the condition in which it was received from the tanner. The potential stretching properties of the shrunken leather are, however,

proportionately increased so that it is possible to stretch the leather itself an amount'80 corresponding to the shrinkage, namely `about 4% or 5% of its area, inl addition to the natural stretch possessed by the leather. As' a result, when the' finished leather' is pulled over the last havin been dipped in With the result that the latter cracks. The 9 0 loss resulting from the cracking of the hn,-

ish in the manufacture of "patent leather shoes is a real one, oftentimes resulting jin large damage claims against the leatherIr-.f c usher and necess1tat1ngthe constant empio l 95 ment of repair operators for repairing t e,

cracked finish as a part of the regular personnel of the shoe manufacturing organization.

lin accordance with the improved process for manufacturing patent leather to `which ther presentinvention is preferably applied,

provision lis made for counteracting the tendency of the leather to shrink when the coating material is hardened, and this is pref- 305 erably accomplished by hardening the coating material in an atmosphere sulliciently humid to cause the leather to remain in'an expanded or stretched conditionv until the coating material has become hardened and H0 firmly bonded with the leather in such condition. v

In detail the preferred process for manufacturing patent leather isdescribed as follows: The tanned hides in the condition in which they are received from the tannery are first subjected to treatment to permit them to absorb moisture, preferably by being hung up in a roomr or chamber in a humid atmosphere. An exact control of the ,humidity is not necessary, but we have found that sutiicient humidity may be produced by injecting steam into the room so that exposure of the hides for a period of a few hours, preferabl about a half a day, ens ables them to a sorb sufficient moisture to permit them te be stretched into a condition of maximum expansion. lVhen the leather to be finished has been degreased at the tannery it has shrunken during the degreasing operationen amount varying from 2%-5% of its original area and it has been found that the preliminary humidiiication of the degreased leather operates to cause the hidesto ex and into the dimensions originally assumed before the degreasing operation When the hideis stretched.

It is preferred to expose the hides to humidity whether they have been previously degreased or not, as by so doing the leather is rendered more susceptible of being completely drawn out when stretched upon the frames, and as a result the finished leather produced is of highest quality, appearance and character, as will be described.

After the hides have been thus exposed to the preliminary humidiication, they are stretched inthe usual manner upon the wooden frames, and then the daub or initial base coat may be applied in the usual manner. When the humidiiied leather is thus stretched upon the frame, the individual hair cells are believed to be opened or expanded, permitting the daub coat to penetrate with better advantage, and to thereby produce a su erior bond between the finish andthe leat er. The daub coat is then I dried, and for this purpose the frame and other suitable manner.

hides are preferably placed in aclosed heated chamber 10 provided with a blower or fan 12 for circulating the air therein and for removing the solvent gases evaporated from the daub coat. The temperature ofthe room is preferably maintained at a low point, approximately 110 F., and in order to prevent any shrinka e in the leather at this time provision is ma e for introducingmosture into the chamber 10, and this may be conveniently accomplished by injecting steam from discharge nozzles 14er in any An excess of humidity appears to have little or no effect upon the rapidity of drying or hardening the daub coat, a period of approximately 12 hours being sufficient for this purpose.

amaze@ After the daub coat has hardened the frames and leather are removed from the dry room 10, and a finishing coat is applied in the usual manner over the daub coat. After the finishing coat has been applied, the frames and leather are )laced in ovens 20, which may, and prefer. )ly will. be of the general construction now employed, having provision for sustaining the frames hori- Zontally therein, one frame superposed above the other, and each spaced a short distance from the next. The ovens are provided vuil h the usual steam coils 22, preferably located ai; the bottom thereof, and during the drying' or -hardening of the finish coat a temperature erably will be provided with means for humidifying the air therein. For this purpose a tank '30 containing Water may be located within the oven at the bottom thereof, and a perforated pipe 32 positioned Within the tank. v

With thi's arrangement steam is supplied to the perforated pipe 82, and the steam emerging through the perforations in the pipe boils the Water in thc tank 30, thus supplying the required humidity. The wa ter Within the tank may be maintained at a constant level by a ball float 34; of usual construction, and the supply of steam to the pipe 32 may and preferably Will be controlled by automatic humidity controllers of any usual or preferred type, the construction and operation of Which are well known and need not be further described. Vith this arrangement the humidity within the oven is preferably maintained during the drying of the finish coat at an amount corresponding to a dry bulb temperature at 150 F. and a Wet bulb temperature of 125 F., but other temperatures With a correspending high humidity are also satisfactory, and in this manner shrinkage of the leather during the drying operation is prevented. It is of advantage to employ a humidifying system as above described in order to revent appreciable circulation of the air Within the oven .during the drying of the finish coat to the end that the surface of the coat may accumulate as little dust and dirt as possible during the drying thereof, but if found desirable other forms of humidifying apparatus may be used.

For finishing certain kinds of leather additional finish coats may be applied in the usual manner, and the coatings dried in 1 ovens 20 employing humidity to prevent shrinkage of the leather. After the finish -coatingshave been applied and dried as above described, the leather may be sun dried or dried by any of the processes herelun tot'ore proposed and because of the fact that the several coatings have been applied to and dried upon the leather while the latter has been maintainedin its expanded condition the final exposure to-the sun does not operate to appreciably shrink the leather, al-` though if desired, before shipment vtheleather may be stood over night in a humidified atmosphere.

From the description thus far it will be observed that the present process is of particular advantage to the tanner or finisher of the leather for thereason that the finished hide has maximum area, and may be sold at a proportionately higher price. For example, inthe ordinary process the sunning and subsequent drying or baking without the use of humidity causes a hide to decrease in area approximately 5%. In other words, the finished hide has lost approximately 5% in area during the finishing and this adds approximately 1% cents per foot to the cost. Inasmuch as an ordinary finishing plant turns out a number of thousand of feet-per day, it will be apparent that the saving is a. real one. In addition, when the leather to be finished has been degreased atthe tannery, it has, as above described, been shrunk during the degreasing anywhere from 2% to 5%. In accordance with the presentprocess this shrinkage is' restored to the hide representing a proportionate saving to the tanner or tothe finisher. l

The most important advantage of .the present process is the fact. that the leather is finished under such conditions that the finished product possesses only sufficient stretch that' it may be successfully drawn over the last in themanufacture of the shoe without stretching the leather beyond what may be regarded as the elastic limit ofthe varnish or finish so that the cracking which oftentimes occurs is prevented. This is very important from the point of view of the shoe manufacturer because the partially inished shoe represents more loss than merely the finished leather itself. As a matter of fact, shoe manufacturers haverefused to pay Vanything for leather which cracks or works poorly in the factory and in. some instances have been known to make damage claims against the tanner for damaged shoes. These damage claims run into large sums of money.

In addition to these advantagesthe present process produces superior finished leather. A In the ordinary process the finishing coats are applied to the leather with the pores of the latter in aclosed. or partially.

closed condition, whereas in the present process the leather is placed in a condition such thatvit may be stretched before the fin.- ishing coats are applied which seems to effect an' openin of the pores, and prevents it from shrinkmgduring the finishing and as a result an improved grainy appearanceis imparted to the leather which adds to the character and isvery important from the Y Y Vsales point of Viewv of the finished leather, inasmuch as the` superior character of the leather commands higher prices. The advantages of the present process may, there fore, be summed vup as follows: The finished leather produced possesses superior appearance, works better ,in the shoe factorles than ordinary finished leather, and the shoes may in the frames when the toggle strings brea.k l

the leather is maintained ina position such as to permit a most uniform drying of the coat. The humidity also adds considerably to the life of the wooden frames and inasmuch as these represent-a substantialinvestment for the leather-finisher, this is an important advantage, of the present process.v In addition, higher temperatures may be used in baking the finished coats without injury to the same. v

The material employed for the various coatings may and preferably will comprise that usually employed for this purpose at the present time, although any material may be employed which is found suitable for producing the desired coatings.

Having thus described the invention, what is claimed'is:

1. In a process of finishing leather, the steps comprising first humidifying the leather, stretching the same, applying coating material to the stretched leather, and

thereafter drying the coating material under conditions which counteract the tendency of the leather to. shrink during the drying operation.

2. In a process of finishing leather, `the steps comprising humidifying the leather, stretching the samefapplying a daub coat vini to the stretched humidified leather, hardening said daub coat ina humidified atmosphere, applying a finishing coat over the daub coat, and thereafter drying the finishing coat in a humidified atmosphere.

3. In a process of finishing leather, the steps comprising applying a layer of coating material to the leather and drying 'the coating material underconditions which counteract the tendency of' the leather to shrink y during the drying operation.

4. .In a process offinishing leather, the

steps comprising applying a daub coat tol the leather, drying the daub coat in a humidified atmosphere without shrinking the leather, applying a finishing coat over the danb coat, and baking the leather to harden the finishing coat Without appreciably shrinking the leather. Y

5. In a process of finishing leather, the steps comprising stretching the leather, applying a coating to the leather While the latter is maintained in a stretched condition,

and thereafter drying the coating under conditions which counteract the tendency of the leather to shrink during the drying operation. l

6. The process of finishing leather-Which consists in humidifying the leather, stretching the same, applying a daub coat to the stretched, humidiied leather, hardening the daub coatv in a humidified atmosphere in a drying chamber, applying a finishing coat over the daub coat, and thereafter hardening the finishing coat in a humidified atmosphere.

7. In the process of finishing degreased leather, the steps which comprise first humidiying the leather to restore the degreasing shrinkage, applying a layer of coating material to the leather, and thereafter drying the coating-under conditions Whichcounteract the tendency of the' leather to shrink during the drying operation.

JOHN B. l/VELCH. WILLIAM C. WELCH. 

